Troui Breeding. 57 



only during the breeding season, and others are so 

 nearly similar that except for the protruding abdomen 

 of the gravid female the sex can be distinguished only 

 by dissection. 



A few, as the sharks and rays, have as distinct marks 

 of sex, as do mammals, such as "claspers," spines on 

 head and fins, etc. ; others, as the Emhiotocoids, or vi- 

 viparous fishes, have a different structure of the anal fin, 

 while the great majority of fishes, especially the fresh- 

 water kinds, have merely a brilliancy or intensity of 

 color during the pairing season, which is invariably con- 

 fined to the males. There is a very common notion 

 prevalent that goldfish can be distinguished by the 

 dorsal fin, that of the male being shorter than that of 

 the female — that is, having not so many rays ; but this 

 is entirely groundless. The dorsal fins of this species, 

 Carassius auratus, are very variable, as in fact the entire 

 fish is, but this variation does not indicate sex in the 

 least, and I do not hesitate to say that this fish is one 

 whose sex cannot be told except by dissection, save 

 when the female is distended with eggs. 



The little Cyprinodonts, killey fishes, show during 

 the spring and summer such great dififerences between 

 the dandy male and its quaker-like mate that they might 

 be mistaken for different species, while most of the 

 percoids, as perch, bass, sunfishes, etc., simply show a 

 difference in the intensity of the colors. In some of the 

 sticklebacks, as Eucalia inconstans, Jordan, the male is 

 gorgeous in red and green during the breeding season, 

 while the more sober bridegroom of the four-spined 

 variety, Apeltes quadracus, contents himself with a 

 small pair of crirnson ventral fins. Most of the cyprin- 

 oids, at other times indistinguishable, can be recognized 

 during the breeding season by brightly-colored fins. 



